Bao H, Jacobs-Helber S M, Lawson A E, Penta K, Wickrema A, Sawyer S T
Department of Pharmacology and Toxicology, Medical College of Virginia campus of Virginia Commonwealth University, Richmond, VA, USA.
Blood. 1999 Jun 1;93(11):3757-73.
We found that erythropoietin (EPO) and stem cell factor (SCF) activated protein kinase B (PKB/Akt) in EPO-dependent HCD57 erythroid cells. To better understand signals controlling proliferation and viability, erythroid cells that resist apoptosis in the absence of EPO were subcloned and characterized (HCD57-SREI cells). Constitutive activations of PKB/Akt, STAT5a, and STAT5b were noted in these EPO-independent cells. PI3-kinase activity was an upstream activator of PKB/Akt because the PI3-kinase inhibitor LY294002 blocked both constitutive PKB/Akt and factor-dependent PKB/Akt activity. The LY294002 study showed that proliferation and viability of both HCD57-SREI and HCD57 cells correlated with the activity of PKB/Akt; however, PKB/Akt activity alone did not protect these cells from apoptosis. Treatment of HCD57 cells with SCF also activated PKB/Akt, but did not protect from apoptosis. This result suggested that PKB/PI3-kinase activity is necessary but not sufficient to promote viability and/or proliferation. Constitutive STAT5 activity, activated through an unknown pathway not including JAK2 or EPOR, may act in concert with the constitutive PI3-kinase/PKB/Akt pathway to protect the EPO-independent HCD57-SREI cells from apoptosis and promote limited proliferation.
我们发现，促红细胞生成素（EPO）和干细胞因子（SCF）可激活EPO依赖的HCD57红系细胞中的蛋白激酶B（PKB/Akt）。为了更好地理解控制增殖和生存能力的信号，对在无EPO时抗凋亡的红系细胞进行了亚克隆和特性分析（HCD57-SREI细胞）。在这些不依赖EPO的细胞中，观察到PKB/Akt、STAT5a和STAT5b的组成性激活。PI3激酶活性是PKB/Akt的上游激活剂，因为PI3激酶抑制剂LY294002可阻断组成性PKB/Akt和因子依赖性PKB/Akt活性。LY294002研究表明，HCD57-SREI和HCD57细胞的增殖和生存能力均与PKB/Akt的活性相关；然而，单独的PKB/Akt活性并不能保护这些细胞免于凋亡。用SCF处理HCD57细胞也可激活PKB/Akt，但不能保护其免于凋亡。这一结果表明，PKB/PI3激酶活性对于促进生存能力和/或增殖是必要的，但并不充分。通过不包括JAK2或EPOR的未知途径激活的组成性STAT5活性，可能与组成性PI3激酶/PKB/Akt途径协同作用，保护不依赖EPO的HCD57-SREI细胞免于凋亡，并促进有限的增殖。
